Short-Term Effect of Ozone Exposure on Small Airway Function in Adult Asthma Patients with PM2.5 Exacerbating the Effect

Ambient ozone (O₃) has been associated with asthma symptoms and exacerbations. The impairment of small airway function leads to worse control, more frequent exacerbations and increased bronchial hyperresponsiveness in asthma patients. However, the impact of O₃ on small airway function in asthma remains underexplored. Our longitudinal observational study enrolled 312 adult asthma patients and collected a total of 399 lung function records. We applied a linear mixed-effects model to analyze the associations between ambient O₃ exposure at different lag days (from lag0 to lag7) and small airway function parameters, including forced expiratory flow (FEF) at 50%, 75% and 25-75% of forced vital capacity (FVC) predicted (FEF50%pred, FEF75%pred and FEF25-75%pred). Significant associations were found between ambient O₃ levels and reductions in FEF50%pred, FEF75%pred and FEF25-75%pred, with the effects being most pronounced for exposure at lag0. Further analysis indicated that fine particulate matter (PM_2.5) and its main components, including black carbon, organic matter, sulfate, nitrate and ammonium, exacerbated the detrimental effects of O₃ on small airway function. Additionally, stronger O₃ effects were found in asthma patients aged over 40 years, those with a body mass index ≥ 25 kg/m², and individuals with allergic asthma. These results provide new insights into the impact of O₃ on small airway function, offering fresh insights into asthma exacerbation mechanisms and underscoring the critical need to address composite pollutants for more effective asthma management.